Never drop an enrolled class from upcoming lessons; delete a guardian's children with them; pin the panel's line spacing

Three fixes from testing the branch.

A group class was only listed when its schedule resolved to exact
datetimes, which needs a class time *and* a duration — both optional on
the offering form, and the schedule note exists precisely so a studio can
write "Tuesdays 4:00pm" instead. A class configured that way vanished
from the list, which is the one thing this feature must never do. So
Offering::sessionStarts() splits "when does it meet" from "how long does
it run" (sessionWindows() is that plus the duration, unchanged), and
SessionSchedule degrades instead of disappearing: dated rows with an open
end when there is no duration, and a single row carrying
Offering::scheduleLabel() when there is no time to derive dates from.
Only a class whose last day has passed drops out.

Deleting a guardian now deletes the children linked to them, releasing
each one's lessons and enrolments first. A child account is login-less
and exists only so the guardian has somebody to book for; without the
guardian nobody can reach it, book for it, or be billed for it, so it was
left stranded on the roster still holding slots. A `handled` set makes
the re-entrant delete_user each child deletion fires a no-op, and stops a
circular link recursing.

The upcoming panel never stated its own line-height, so a theme setting
line-height: 0 above it — the usual icon-font reset — was inherited
straight through. Below 1 that produces both reported symptoms at once:
stacked lines overlap, and the status pill's background is shorter than
the text in it. Pinned at the same id-level specificity as the rest.

Tests: composer test (863), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 5 <[email protected]>

assets/css/frontend.css

@@ -104,18 +104,41 @@
  * explicit flex rules above, but the text itself still sits in inline elements
  * a theme is free to take out of normal flow — an absolutely positioned,
  * floated or negatively offset span drops the date/time on top of the title and
- * the status pill on top of the Cancel button. Pinning the three properties
- * that would have to change keeps the leaves in flow, at the same id-level
+ * the status pill on top of the Cancel button. Pinning the properties that
+ * would have to change keeps the leaves in flow, at the same id-level
  * specificity the rules above rely on.
+ *
+ * `line-height` is pinned for the same reason and is the subtler one, because a
+ * theme does not have to target this panel to break it — it is inherited, so a
+ * `line-height: 0` anywhere above (the usual icon-font or sprite reset) reaches
+ * these elements untouched. Below 1 it produces both halves of the same bug: a
+ * line box shorter than its glyphs, so stacked lines in the details column
+ * overlap, and an inline-block pill whose background is shorter than the text
+ * sitting in it. Nothing here should ever inherit a line-height, so the panel
+ * states its own.
  */
+#us-booking-app .us-my-lesson,
+#us-booking-app .us-my-lesson-info,
+#us-booking-app .us-my-lesson-actions,
 #us-booking-app .us-my-lesson-title,
 #us-booking-app .us-my-lesson-when,
 #us-booking-app .us-my-lesson-duration,
 #us-booking-app .us-my-lesson-who,
+#us-booking-app .us-my-lesson-kind,
+#us-booking-app .us-lesson-status {
+    line-height: 1.45;
+}
+
+#us-booking-app .us-my-lesson-title,
+#us-booking-app .us-my-lesson-when,
+#us-booking-app .us-my-lesson-duration,
+#us-booking-app .us-my-lesson-who,
+#us-booking-app .us-my-lesson-kind,
 #us-booking-app .us-lesson-status {
     position: static;
     float: none;
     margin: 0;
+    vertical-align: middle;
 }
 
 /*